1. Field of the Invention
In one of its aspects, the present invention relates to a surgical needle, more particularly to a needle for expressing bone cement into a vertebral body. In another of its aspects, the present invention relates to a method for passing a needle into a vertebral body.
2. Description of the Prior Art
Percutaneous vertebroplasty involves the injection of a bone cement or suitable biomaterial into a vertebral body via percutaneous route under X-ray guidance. The cement is injected as a semi-liquid substance through a needle that has been passed into the vertebral body, generally along a transpedicular or posterolateral approach. The three main indications are benign osteoporotic fractures, malignant metastatic disease and benign tumours of the bone.
Percutaneous vertebroplasty is intended to provide structural reinforcement of a vertebral body through injection, by a minimally invasive percutaneous approach, of bone cement into the vertebral body. See, for example, Cotton A., et al xe2x80x9cPercutaneous vertebroplasty: State of the Art.xe2x80x9d Radiograhics March-April; 1998, 18(2):311-20; discussion at 320-3. Percutaneous vertebroplasty can result in increased structural integrity, decreased micromotion at the fracture site, and possibly a destruction of pain fibres due to the heat of the bone cement as it polymerizes and sets. Complete pain relief can be achieved in up to eighty percent of patients. As known to those of skill in the art, the cement should have properties that, when injected, can increase vertebral body stiffness and compressive strength. It is generally preferred that the cement is liquid enough to flow into fracture planes and to fuse them. There is some debate about the appropriate thermal properties, but it is believed by some that the heating effect can be beneficial and cause death to local nerve endings involved in pain stimulation. It is generally accepted that most pain relief is achieved due to increased structural integrity.
Generally, when performing vertebroplasty, a needle of an appropriate gauge (such as eleven gauge or thirteen gauge in a smaller vertebral body) is passed down the pedicle until it enters the vertebral body and reaches the junction of the anterior and middle thirds. Great skill is usually required to insert the needle at a suitable angle and pass the needle through the periosteum, down the pedicle and into the vertebral body. Also, insertion of the needle generally requires a large applied force. Specifically, a large force can be required when entering the cortex and in the transition from the pedicle to the vertebral body.
A suitable cement is prepared, injected through the needle and into the vertebral body, under lateral X-ray projection fluoroscopy imaging. The injection is stopped as the cement starts to extend into some unwanted location such as the disc space or towards the posterior quarter of the vertebral body, where the risk of epidural venous filling and hence spinal cord compression is greatest. The injection is also discontinued if adequate vertebral filling is achieved.
In many needles of the prior art, there is a step or change in the angle of the taper at the needle tip. This change in the taper can cause an increase in the required applied force when inserting the needle. The additional applied force can result in a rib fracture. Thus, needles of the prior art can be difficult to insert into the patient. Presently, it is common for a hammer to be used to overcome the force required to insert the needle into the vertebral body.
During insertion of the needle, operator control is reduced due to the greater required applied force. Further, needles are difficult to accurately insert because of the large required applied force.
Prior art needles used in vertebroplasty have certain limitations. Needles such as the MDTECH, bone marrow biopsy/aspiration needle, ref DBMNJ1104T, from Medical Device Technologies, Inc, 3600 S.W. 47th Avenue, Gainsville, Fla. 32608, have been used for the delivery of bone cement. These needles are designed for obtaining biopsy samples and not for injection of cement. The end of the needles are tapered which can reduce the volume of bone cement injected. On average, about 4 to 5 cm3 of cement can be injected per side. Further, the tip of the needles have a step or a change in the angle of taper, as discussed above, thus making them difficult to insert as resistance is encountered both at the tip and at the step. A large force is required first for the tip to pierce the periosteum and the cortex, and second, a greater force is required for the step of the needle to pass through the periosteum and cortex. Again, additional force is required for the needle tip to pass through the transition from the pedicle to the vertebral body and an even greater force is required for the step of the needle to pass through this transition.
There are many other biopsy needles that can be used for the injection of cement, however these needles suffer from certain limitations. Many needles are used for retrieving soft-tissue biopsy samples and are not suitable for piercing hard tissue such as bone. Also, many needles do not have an end suitable for attachment of a syringe. Further, these needles may not have a handle suitable for applying sufficient force to pierce the cortex or to pass the transition from the pedicle to the vertebral body. Also, many biopsy needles have an end with an internal taper that can reduce the volume of cement that can be injected.
Other needles for use in vertebroplasty are disclosed in International publications numbers WO 99/18865 and WO 99/18866. These instruments include a self-tapping, threaded stylet end for tapping into hard tissue. A cannula fits over the stylet and the threaded end is used to draw the cannula into the desired position. A syringe can be attached to the cannula for injection of the cement. The stylet of this needle is rotatably screwed into the desired position. When the stylet is in the desired position, the cannula is rotatably screwed into position. Alternatively, the stylet can be pushed into the desired position or can be positioned by a ratchet assembly and action.
During insertion of these needles, more control can be gained by the slow rotation of the stylet into place, followed by the cannula being moved into place. Therefore, greater time is required to insert this needle than those needles of the prior art. Also, the needle construction is somewhat complex. The screw portion of the stylet can break off in hard bone or can slide on hard bone.
Thus, there exists a need in the art for cement delivery needle which can withstand the rigours of insertion in a patient dur percutaneous vertebroplasty. It would be desirable if such a needle could be readily constructed and readily put into use by those of skill in the art.
It is an object of the present invention to provide a novel cement delivery needle which obviates or mitigates at least one of the above-mentioned disadvantages of the prior art.
It is another object of the present invention to provide a novel method for passing a needle into a vertebral body.
In one aspect of the present invention, there is provided a cement delivery needle, for use in performing vertebroplasty, having a sheath and an insert. The sheath has an inlet to receive a bone cement and a tapered outlet for expressing the cement into a vertebral body. The insert is receivably removable within the sheath. The insert also has a tip that is alignable with the outlet, when the insert is inserted into the sheath, to present a continuous edge.
In another aspect of the present invention, there is provided a method for performing vertebroplasty on a vertebral body. A cement delivery needle is inserted into a patient, the cement delivery needle having a sheath with an inlet to receive a bone cement and a tapered outlet for expressing the cement into the vertebral body. An insert is receivably removable within the sheath. The insert has a tip that is alignable with the outlet when the insert is received by the sheath to present a continuous edge. When the edge is inserted into a resistant material, an application of force to the needle creates an opening in the material to allow the needle to pass therethrough. The needle is passed down a pedicle and into the vertebral body. The insert is slideably removed from the sheath while maintaining the sheath in the vertebral body. A suitable injector is connected to the sheath. The bone cement is injected through the sheath and into the vertebral body.
In still another aspect of the present invention, there is provided a method for passing a needle into a vertebral body. The needle has a sheath with an inlet and a tapered outlet. The needle also has an insert that is receivably removable within the sheath. The insert has a tip that can be inserted into the sheath and aligned with the outlet to present a continuous edge. The method comprises the steps of piercing the skin lying above the periosteum of a vertebrae along a transpedicular approach. Next, a first force is applied along the needle to cause the edge to pierce the periosteum and cortex and create an opening large enough for the needle to pass therethrough. The needle is then passed through a pedicle. A second force is applied to the needle to cause the edge to pierce a junction of the pedicle and the vertebral body to create an opening of sufficient size to allow the needle to pass therethrough. The needle is then passed into the vertebral body.